When I go to the boot menu on my computer and select USB stick, the screen goes black and there comes a flickering underline. Like I could write something. But I can't. Whatever I push, nothing happens. Except the PrintScrn/SysRq button. When I push it, mu computer beeps. I get no choose menu. Nothing.

I found out the usb stick is in msdos format. So what format should I use and how can I format it? I am not a computer geek who knows everything. I'm just a beginner. And only 16 years old.

I've got a new problem. The screen isn't black anymore. Now there comes an error message:

You might be better off installing from CD, can you try this? The documentation is better for CD. Here is how to do it, and here is how to troubleshoot problems. From your last edit it looks like you are having a hardware problem with the USB stick, and there isn't much you can do about this except to try a different USB drive or port. Good luck.
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Tom BrossmanJun 28 '12 at 7:14

Msdos file system should be fine. Black screen suggests the USB is not bootable, although on many computers the BIOS would at least tell you that it can't find an OS, rather than just show you a flashing cursor. How did you make the USB?

If you need a software to make the bootable USB, you have several choices. All of the below will let you create an Ubuntu Live USB, or a wide variety of other distros or rescue disks.

Cross-platform

Linux Only

I really like LiveUSB MultiBoot. It's a little more complex, but it lets you install several OSes on one USB key. The GUI is not great, and the download site is in French, but if you know what you're doing, it's very powerful.

Windows Only

I haven't used this before, but LinuxLive USB Creator doesn't look too bad (judging from screenshots and information on the website).